Gaseous-conduction apparatus



Aug. 7, 1928.

C. G. SMITH GASEOUS CONDUCTI ON APPARATUS Filed June 13, 192'! rmmlau v,192s.

UNITED STATE a 1,679,449 PATENT OFFICE.

m G. SIITH, OI miI'ORD, IASSACKUSETTS, ASSIGN OR TO RAYTEEON INCQOI'CAIBBIDGI, IASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

GASEOUS-CONDUCTION APPARATUS.

Application filed June 18,

The present invention relates to electrical apparatus and in particularto unilateral conduction devices which employ a confined bod of as ascarrier for the space current.

5 N otwit standing the fact that the tube art in general has reachedahigh state of development, there still remains instances of tube failureand short life due frequently to disintegration of material forming theelectrodes. Indeed, with the improvements heretofore offered in the artof evacuation and sealing, the roblem of tube life now centers almostentirely about the stability of electrodes, particularly the anode. The

i erosion of this member is most pronounced in devices which depend upngas, usually of the monatomic group for conduction, operating on theionization principle, and is caused in part by reverse current tendingto substitute the normal function of one electrode, specifically thecathode, for that of the other.

While there are many factors involved, of more or less importance, Ifound the greatest improvement in securing commercially long electrodelife to reside inthe relation of gas filling and anode material, moreespecially in a specific combination of these elements. a

The primary object of my invention is to provide space current apparatushaving relatively long'life'. A more specific object is to improvecertain of the elements within the tube with a view towards minimizingerosion of electrode material under conditions of heavy ion bombardmentand other deleteri ous effects. With these and other objects in view,reference should now be had to the following description which, whenread in connection with the accompanying drawing, represents oneembodiment of the present invention. While my invention has applicationto all space current apparatus, in the interests of clearness, I proposeto exemplify the subject matter by referring to a specific form ofrectifier; thus in the figure there is shown a space current devicesimilar to that in the Smith Patent No. 1,617,179 and the Jenksapplication Serial No. 752,867.

This type of rectifier employs an envelope 1 which may be formed ofglass, a hollow cathode 2 of tantalum or other refractory material,anode 3, insulating thimbles 4 preferably of lavite and a basecompyrising metal- 5 he cylinder 5, secured by suite le compound 1987.Serial No. 188,888.

projections and held'in position by cathode 2. The anodes are mounted inopenings in members 4 concentrically with projections 8 and openings 9in the cathode. The cathode is preferably formed in two parts, the upperpart comprising a conic'ally shaped element and the lower part 10 acover fitting the'open end of the cone. A portion of each thimble 4. isspaced from the anodes a distance materially less than the mean freepath of the electrons present and serves to prevent the passage ofcurrent between either anode and the outer surface of the cathode.Ionization is thus confined to the space enclosed by the cone, i. e. theregion adjacent to the inner surface of the cathode. In order tominimize the internal losses of the device I may coat the active portionof the cathode with a substance as alkali, earth alkali or combinationof the two, to increase emission. If desired, the substance may beconveniently applied in the form of a nitrate,

successively heating the cathode, e. g. by a hydrogen flame, to hightemperature (e. g.

above 1000 centigrade) and spraying the solution onto the cathode asdisclosed and claimed in the application of P. L. Spencer,

Serial No. 183,045. A number of coats may be applied in this manneruntil the alkali substance permeates and alloys with the metal of thecathode giving a lasting effect by way of low work function. Thecylindrical members 4 contain circular recesses 11 adjacentto-the-openings 9 to prevent or reduce to a negligible factor thetendency of current to flow between cathode and either anode along thesurface of insulation. The openings 9 are of such size as to provide 1space between the cathode and operating anodes, comparable to orslightly less than the mean free path of electrons within the region ofthe cathode. While the cathode may be supported solelyby cylindricalmembers 4:, I prefer partly to depend for support" on the centrallylocated cathode lead 12 v which is joined electrically to one of theconnector plugs.

Now, whereas in the patent and application supra, it was stated that thepreferred gas of the monatomic group was helium under the pressure ofseveral millimeters and that the anodes could be satisfactorily made ofmany refractory conductors, it was found in practice that when immersedin helium, these metals ofi'er a widevariation of disintegrationaleffects at the anode under similar conditions of operation. In thisconnection I have discovered one outstanding example giving an electrodelife nearly ten times that of the nearest combination; I have referenceto the use of tantalum for anode material in a helium filling such asmentioned which arrangement appears to cooperate in an unusual,unforeseen and inexplicable'manner'to minimize electrical disassociationat the positive mem her. It was further verified that the remarkablebehavior between these substances is quite independent of the shape,size and type of apparatus, the superiority of operation beinaccentuated under low gas pressure and high voltage,'a conditionparticularly harmful toother combinations. When utilizing tantalum foranode material in an atmosphere of helium one may substantially decreasethe gas pressure and increase applied potential over the ordersofmagnitude now commonly employed in the art without fear of materiallyshortening the life of the apparatus through electrode failure. Thepreferred pressure of gas may be of the limitations are to. be imposedon my invention as defined by the following clainis except as may benecessary in view ofprior a,

I claim: a

1. In a aseous discharge apparatus of the type. escribed containinghelium, an anode, a cathode operatively associated therewith, said anodecomprising tantalum.

2. A gaseous discharge rectifier containing helium, a hollow cathodehaving an opening therein, another electrode presented to the interiorof the cathode through said opening, said other electrode comprisingtantalum.

Signed by me at Cambridge, Massachusetts, this 6th day of J uzie, 1927.

CHARLES G. SMITH.

